Although IPv6 has not yet been used in large scale at present, with the fast lack of global IP addresses and business requirements, the rapid development and gradual popularization of IPv6 have become inevitable. But how to transition to IPv6 is also an important subject, and a IPv4/IPv6 dual stack mode is one of common transition mechanisms.
For the dual stack mode, selection of IP modes is involved inevitably when a terminal initiates services, and in general, services are accessed using a domain name mode, so domain name resolution becomes a key point.
In a scene of IPv4 and IPv6 dual stack, there will be two DNS (Domain Name System) resolution request modes, mode A and mode AAAA when a terminal initiates a domain name request. The mode A corresponds to a request in an IPv4 address format and the mode AAAA corresponds to a request in an IPv6 address format.
On this premise, when a dual stack terminal accesses to a domain name, a strategy for sending DNS resolution requests generally is to constantly and continuously make the requests using the two modes, i.e. first the mode A then the mode AAAA, or vice versa. Since an IP address mode corresponding to a domain name in a reality scene in network environment is relatively fixed, one of two continuous requests made in the two modes will generally fail. If the service to be accessed only supports IPv6 addresses, a domain name server will certainly fail to respond to the first DNS resolution request in the mode A, and will respond correctly, with an IPv6 address format, to the second DNS resolution request in the mode AAAA initiated by the dual stack terminal. So when the dual stack terminal accesses to IPv6 services, the efficiency will be affected. On the contrary, if the DNS requests are always made in the mode AAAA first and then in the mode A, then the effect is not ideal when IPv4 services are accessed.